A user info was incorrect and profile sync was not updating. So I deleted the user from the user profile (Central admin). I did a full sync but that user did not make it in the profile database. How do I restore this deleted user back in the profile database.
It would be hard to restore deleted users instead you will have to restore the whole profile database. I would highly recommend laying a complete rollback plan before you proceed with restoration.
The only way to restore you users is to restore the previous back up of profile database. After restoration, reset the IIS and you are good to go!
But, if it is one user, it's better to create it manually.